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W HU07713 2 F METALIZED FILM RESISTOR 13 kohm, . W HK05715 1 J CARBON RESISTOR 15 kohm, . W HK05733 1 J CARBON RESISTOR 33 kohm, . W IG06920 3 IC AMP MJM2041DD HT56009 1 B SEMI-FIXED VR (TRIMMER) 50 kohm IF00004 2 DIODE 1S1555 IF00214 1 ZENER DIODE RD5.6ED2 VA25610 1 B SLIDER VR (FADER) 10 kohm Table 6-1. Parts List for Making Remote VCA Control Circuit Figure 6-18. VCA Control Voltage versus Fader Position Page 6-19 Section 7 Operating Notes and Hints . Operating Notes and Hints This section is not meant to be comprehensive. Instead, it focuses on a few areas which we feel require special attention, or where a better understanding of the function can lead to far more utility or better sound quality from the PM4000. 7.1 Console Gain Structure In the GAIN STRUCTURE AND LEVELS section of this manual, we discuss some general considerations regarding levels and system setup. What of the proper gain structure within the PM4000? How can the many faders and other level controls that affect a given signal all be adjusted for the optimum results? These are important questions to ponder, and we hope you will take some time to study the possibilities. 7.1.1 What Is The Proper Gain Structure? Let’s begin with the XLR channel input to the console. According to the INPUT CHARACTERISTICS chart in the SPECIFICATIONS section, the nominal input level ranges from -70 dBu (0.25 mV) to +10 dBu (2.4 V). These are the levels that will supply the ideal signal level throughout the module with the PAD set to 0 dB or -30 dB, the input GAIN control as required, fader set to its nominal position, and no VCA groups assigned. Actually, a wider range of levels can be accommodated if the fader is adjusted to other-thannominal position; from -90 dBu (0.025 mV) minimum to +24 dBu (12.3V) maximum. What is the correct gain structure? Simply stated, it is the level at which there remains adequate headroom so that peaks can be accommodated without clipping, while at the same time there is sufficient “distance” above the noise floor that noise does not become objectionable. If a signal is too high in level (too “hot”) at a given point in the console, then peaks or, in the extreme, the entire signal, will be subject to distortion. If the signal is too low in level, there may be considerably more headroom and less risk of distortion, but the noise will be that much more noticeable, and quiet passages may be masked entirely by residual noise. The “ideal” level, then, where headroom and noise tradeoffs are optimum, is also known as the nominal level. There is no single value for the correct nominal level; it varies throughout the console. This is what the middle graph line in the GAIN STRUCTURE chart in Figure 3-?? depicts. The top graph line indicates the clipping point. The distance between these two lines, at any point along the horizontal signal flow scale, depicts the available headroom. It is important that wide headroom be available throughout a console, not just at the input and output; otherwise multiple signals applied to the busses may add together such that the mixed level approaches clipping, even though the individual feeds to the mix are within their acceptable nominal range. Sometimes a group or master fader can be adjusted to correct this condition, other times it cannot because the distortion is occurring in an amplifier ahead of the fader, and the only cure is to lower the signal levels applied to the bus. How can one know the best course of action when distortion, or excess noise, is encountered? 7.1.2 What Affects Gain Structure? First, understand that signal levels can be increased by either increasing amplifier gain (including EQ boost), reducing the amount of attenuation, or adding multiple signals together. Similarly, signal levels can be reduced by either decreasing amplifier gain (including EQ cut), increasing the amount of attenuation (including filter roll-off), or splitting the signal to feed two or more circuits. With this in mind, it becomes clear that the mere act of feeding the “correct” nominal level signal into a console is no guarantee that it will remain at an acceptable level throughout the console. 7.1.3 Establishing The Correct Input Channel Settings In the case of the PM4000, the input channel meter LEDs [20] [20S] make it relatively simple to obtain the correct gain structure at the input stage. Begin with the PAD set at maximum attenuation (-30 dB), the GAIN control centered, and apply the typical input signal to the channel input. If none of the meter LEDs are illuminated, or perhaps just the -20 LED, disengage the attenuation PAD switch to remove the 30 dB of attenuation. Adjust the GAIN control as required so that the red PEAK LED flashes on only occasionally, during the loudest program peaks, and the 0 LED flashes frequently or remains on. This establishes the correct channel sensitivity for the initial setup (you may wish to alter these values during an actual program mix, as explained in subsequent pa...

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